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Abstract

Background

Prevention of childhood asthma is an important public health objective. This study
evaluates the effectiveness of early detection of preschool children with asthma symptoms,
followed by a counselling intervention at preventive child health centres. Early detection
and counselling is expected to reduce the prevalence of asthma symptoms and improve
health-related quality of life at age 6 years.

Methods/design

This cluster randomised controlled trial was embedded within the Rotterdam population-based
prospective cohort study Generation R in which 7893 children (born between April 2002
and January 2006) participated in the postnatal phase. Sixteen child health centres
are involved, randomised into 8 intervention and 8 control centres. Since June 2005,
an early detection tool has been applied at age 14, 24, 36 and 45 months at the intervention
centres. Children who met the intervention criteria received counselling intervention
(personal advice to parents to prevent smoke exposure of the child, and/or referral
to the general practitioner or asthma nurse). The primary outcome was asthma diagnosis
at age 6 years. Secondary outcomes included frequency and severity of asthma symptoms,
health-related quality of life, fractional exhaled nitric oxide and airway resistance
at age 6 years. Analysis was according to the intention-to-treat principle. Data collection
will be completed end 2011.

Discussion

This study among preschool children provides insight into the effectiveness of early
detection of asthma symptoms followed by a counselling intervention at preventive
child health centres.

Trial registration

Current Controlled Trials ISRCTN15790308.

Background

Asthma (symptoms)

Asthma is a highly prevalent chronic condition associated with considerable morbidity,
reduced health-related quality of life (HrQoL) and significant costs for public health
[1-6]. The World Health Organisation (WHO) defines asthma as a chronic inflammatory disorder
of the airways associated with increased bronchial hyperresponsiveness [1]. The WHO recently estimated that worldwide about 300 million people suffer from asthma
[1]. The International Study of Asthma and Allergies in Childhood (ISAAC) showed marked
variations in the prevalence of childhood asthma between countries [5]. On average, 10% of European children suffer from asthma [1].

In preschool children it is difficult to diagnose asthma because symptoms are non-specific
and additional tests are not yet possible. Therefore, a symptom-based rather than
a diagnosis-based approach has been applied [7]. In preschool children asthma symptoms are commonly defined as wheezing, shortness
of breath or dyspnea [8-10]. An asthma diagnosis is often preceded by asthma symptoms in the first years of life.
In the Netherlands, the Prevention and Incidence of Asthma and Mite Allergy (PIAMA)
study reported a wheezing prevalence of 21% in the children's first year, rapidly
falling to 4% in the 4-5th years of age [11].

Child Health Care

Asthma symptoms are regularly underreported, and children often remain undiagnosed
and/or undertreated [12-15]. The Netherlands has a unique preventive child health care system, i.e. about 90%
of all children (aged 0-4 years) are periodically monitored in a nationwide programme
at set ages [16]. This programme is offered free-of-charge by the government and participation is
voluntary [17]. However, until now, no systematic early detection and counselling intervention of
asthma symptoms has been applied in preventive child health care.

Objectives

This study evaluates the effectiveness of early detection of asthma symptoms in preschool
children in preventive child health centres. Our hypothesis is that early detection
of asthma symptoms (at ages 14, 24, 36 and 45 months) followed by a counselling intervention
at the child health centre, will reduce the prevalence and severity of asthma symptoms
and asthma, and also improve HrQoL at age 6 years [18-21].

Methods/design

Design and setting

This cluster randomised controlled trial (RCT) is embedded in the Generation R study,
in collaboration with the regional Child Health Care Organisation Ouder & Kindzorg in Rotterdam. The Generation R study is a prospective population-based cohort study
running from fetal life until young adulthood. The Generation R study is designed
to identify early environmental and biological determinants of growth, development
and health in fetal life and childhood; study details have been published [22-25].

The present study was conducted in accordance with the guidelines proposed in the
Declaration of Helsinki, and is approved by the Medical Ethical Committee of the Erasmus
Medical Centre. Written consent was obtained from all participating parents.

Participants

The Generation R cohort included 9778 pregnant women living in Rotterdam, the Netherlands.
The participating women gave birth to 9745 live-born children between April 2002 and
January 2006. A total of 7893 children participated in the postnatal phase [25]. The cohort for the early detection and counselling intervention of asthma symptoms
consisted of all 7775 children participating in the postnatal phase of the Generation
R study and living in the intervention area (Rotterdam-North, defined by postal codes
3010-3070) (Figure 1).

Figure 1.Study design. The flow of participants through the randomised controlled trial for early detection
of asthma symptoms and application of the counselling intervention.

Randomisation

Randomisation was done at the level of the child health centres. First, the child
health centres were ranked based on the socioeconomic status of their neighbourhood.
Child health centers in each subsequent couple in this list were randomly assigned
to the intervention group (n = 8) or the control group (n = 8) (Figure 1).

Intervention Condition

A - Early detection

At the intervention centres the physician (for children aged 14, 36 and 45 months)
or the nurse (for children aged 24 months) performs the early detection tool in an
interview with the parents during the regular visits. On average, the interview takes
about 1 minute. There are 6 questions: 4 adapted from the ISAAC on the presence of
asthma symptoms during the past 4 weeks and the past 12 months [26,27], and 2 on the use of anti-asthma therapy during the past 4 weeks prescribed by the
general practitioner (GP) or paediatrician, and on tobacco smoke exposure [26]. Details on this early detection tool are given in Additional file 1.

Additional file 1.Early detection tool for early detection of asthma symptoms in preschool children. The file contains the early detection tool (consisting of 6 questions).

B - Counselling intervention: Personal advice

When parents reported that their child had at least 3 episodes of asthma symptoms
during the past 12 months and at least 1 episode of asthma symptoms in the past 4
weeks, they received an information leaflet concerning asthma. If the child had been
free of asthma symptoms during the past 4 weeks, the physician advises a visit to
the GP should the child's asthma symptoms return. If the child had been exposed to
tobacco smoke, the physician/nurse advises parents to prevent this, and provides them
with an information leaflet about preventing their child from exposure to smoke. Physicians/nurses
at the child health centres use environmental (anti-asthma home) intervention guidelines
for children already diagnosed with an allergy (Guidelines of the Dutch College of
General Practitioners) [10] (see Additional file 2).

Additional file 2.Counselling intervention scheme following early detection of asthma symptoms (I) and
tobacco smoke exposure (II). The file contains an overview of the steps of counselling intervention, following
early detection of asthma symptoms (I) and tobacco smoke exposure (II) in preschool
children.

C - Counselling intervention: Referral

When parents reported that their child had at least 3 episodes of asthma symptoms
during the past 12 months, of which at least 1 in the past 4 weeks, and the child
has not yet been treated by the GP or paediatrician in the past 4 weeks, the child
is immediately referred to the asthma nurse at the regional Health Care Organisation
and the GP. If the child has already been treated by the GP or paediatrician in the
past 4 weeks, the child is referred to the asthma nurse only (Additional file 2).

Control condition

The 'control' child health centres followed current routine practice. Although parents
might spontaneously mention asthma symptoms, or the physician/nurse might notice asthma
symptoms, no active effort was made by the study team to facilitate detection of asthma
symptoms in the control centres.

Measurements

Baseline assessment

Information on asthma symptoms was obtained via questionnaires at age 6 and 12 months,
and yearly thereafter. Questionnaires were completed by the parents until the age
of 6 years. Wheezing and breathlessness were measured with items adapted from the
ISAAC [28,29]; the question on persistent phlegm ("having had phlegm on at least 4 days per week
for at least 3 months") was based on the American Thoracic Society questionnaire for
respiratory symptoms in childhood [29]. Information on parental smoking at baseline was obtained via a questionnaire during
pregnancy, before randomisation.

Primary outcome

Both the intervention and control group are followed, and outcomes at age 6 years
are compared to evaluate the effectiveness of early detection and counselling intervention
of asthma symptoms. At age 6 years it is still difficult to diagnose asthma due to
the absence of a gold standard. However, in many children with transient wheezing
conditions other than asthma, the symptoms will have disappeared by this age; moreover,
an asthma diagnosis is more accurate at age 6 years than in preschool children.

The following items (obtained via questionnaires) are used for the case definition
of asthma: 1) at least 1 reported episode of wheezing, 2) inhaled steroids prescribed
by a physician, 3) a parental report of a physician's diagnosis of asthma at any time
plus a parental report of asthma during the past 12 months.

In the analyses, children are considered positive for asthma only if they have one
or more positive items at the ages of 45 months and 6 years [30].

Secondary outcomes

Supplementary to this dichotomous primary outcome (asthma yes or no) we use continuous
outcomes at age 6 years: i.e. frequency and severity of asthma symptoms, and HrQoL
variables, obtained via questionnaires. To assess the overall impact of early detection
and counselling intervention of children with asthma symptoms on HrQoL, the 28-item
child health questionnaire 'parent form' (CHQ-PF28) is used at age 6 years [31].

At age 6 years, children are tested with i) measurement of fractional exhaled nitric
oxide (FeNO), a marker of eosinophilic airway inflammation which is elevated in atopic
asthma, and ii) Rint, a lung function test that measures interrupter resistance of
the respiratory system [32]. Other outcomes obtained via questionnaires at age 12, 24, 36 and 48 months include
HrQoL (the Infant-Toddler Quality of Life Questionnaire, ITQOL) at age 12, 24 and
48 months [33,34], and the Health Utilities Index Mark 3 (HUI3) at age 36 months [35-37].

Co-variates

Information on parental characteristics (age, ethnicity, educational level, household
income, allergy, and presence of other conditions or diseases) are obtained from the
first questionnaire at enrollment in the study. Parental smoking habits are assessed
via questionnaires when the child is aged 6, 24 and 36 months, and 6 years. Child's
birth weight, date of birth, gestational age and gender are obtained from national
midwife and obstetrician registries. Breastfeeding and presence of pets are assessed
by questionnaire at age 6 months. Other child characteristics (age, presence of siblings,
day-care attendance, eczema, allergy, respiratory and non-respiratory tract infections,
presence of other conditions or diseases, frequency and severity of asthma symptoms,
and prevalence of physician-diagnosed asthma) are obtained via questionnaires at the
age of 12, 24, 36 and 48 months, and 6 years.

Power of the study

Net 7775 children will visit the 16 participating child health centers. Considering
a visit response of 90% [16] and assuming a loss-to-follow up of 30%, at least 2450 children per group will participate
in outcome measurement at 6 years. Taking into account cluster randomization, assuming
a prevalence of asthma of 12% in the control group at age 6 years [38,39], alpha 0.05 and a power of 0.80, an absolute difference in the prevalence of children
with asthma between intervention and control group of 2.25% (12% asthma diagnosis
in the intervention group, 9.75% asthma in the control group) can be established with
a total of 16 child health centers/7775 children starting in the study at age 14 months.

Statistical analyses

The effectiveness of the early detection tool for asthma symptoms is evaluated on
an intention-to-treat principle [40]. Multi-level analyses are applied to allow for dependency between the individual
measurements within the 16 randomised child health centres [41,42]. Outcomes (primary and secondary) are analysed by means of logistic regression analysis
with independent variables: intervention or control group, gender, age, socioeconomic
status, ethnicity, exposure to tobacco smoke, pets, siblings, co-morbidity (e.g. eczema,
allergy, respiratory and non-respiratory tract infections). Interaction effects of
gender, social disadvantage and ethnic background are examined. Complementary subgroup
analyses are done for gender, socioeconomic status and ethnicity. The impact of early
detection and counselling intervention of asthma symptoms, as compared with the control
group, is analyzed by means of multiple linear or logistic regression analysis, for
continuous or dichotomous outcome variables, respectively [42]. A non-response analysis is conducted to determine possible selection bias. In the
non-response analysis the following characteristics of (non)-participating children
and their parents are taken into account: gender, ethnicity, socioeconomic status,
frequency of asthma symptoms, exposure to tobacco smoke, use of asthma therapy, and
abnormal lung auscultation. The trial is reported according to the CONSORT standards
for reporting RCTs [41]. Statistical analyses are performed using the Statistical Package of Social Sciences
version 17.0 for Windows (SPSS Inc, Chicago, IL, USA).

Discussion

We present the design of a cluster RCT for early detection of asthma symptoms in preschool
children, followed by a counselling intervention at preventive child health centres.
Although asthma often starts in early childhood [43,44], in most preschool children asthma can not reliably be diagnosed [18,45]. On the other hand, many young children do have asthma symptoms, and asthma may be
underdiagnosed and/or undertreated in this group [14,46]. Diagnosing asthma is difficult in preschool children due to the nonspecific symptoms
and because conventional lung function tests cannot be carried out [7].

Until now, there is no evidence that early detection and counselling interventions
at young age alter the natural course of asthma [44]. However, it is known that impaired lung function is related to the length of the
asthma disease process [47]. So far, evidence suggests that intervention during the early stages of asthma is
important [47].

This study aimed to evaluate an early detection tool that is based on symptoms, and
followed by a counselling intervention. The goal is to apply an early detection and
intervention programme in child health centers to promote timely detection of asthma
symptoms in preschool children, and thereby improve their wellbeing and HrQoL.

The ISAAC core questions were originally designed for epidemiological studies in children
aged 6 years and over, and not for individual case-finding purposes. However, we used
selected questions on the frequency of asthma symptoms, adapted from the ISAAC core
questionnaires as they were originally used in the Dutch PIAMA cohort [48]. It remains debatable whether or not parents' reports on asthma symptoms are accurate
[49-51]. Some state that asthma symptoms are reported with low or moderate accuracy [52,53], whereas others found that, compared with paediatricians' records, parents were able
to report asthma symptoms accurately, especially for young children [54]. We decided to use early detection of the child's asthma symptoms by means of parental
reporting, obtained via an interview conducted by the physician or nurse. As an early
detection tool, parent-reported questionnaires are non-invasive, inexpensive and reliable.
However, the impact of this programme remains to be shown and can only be accomplished
based on a RCT, such as the present study.

The strengths of the present study are the size of the study population, the randomised
controlled design conducted in the practice setting (which will facilitate implementation
if the programme proves effective), information on numerous potential mediating factors/confounders,
and the regular free-of-charge visits [16]. Children visit the child health centres at set ages, which offers optimal opportunity
to provide tailored asthma symptom counselling.

Although lung function can be applied, and symptoms become more specific at age 6
years, it remains difficult to diagnose asthma at school age. The definition of asthma
remains arbitrary and mainly symptom based. However, an asthma diagnosis is more evident
at age 6 years compared to preschool age. Therefore, the primary end-point in this
study is asthma (yes or no) at age 6 years, defined as parent-reported asthma symptoms,
medication, or both at different ages, because the aim was to detect persistent asthma
symptoms with clinical relevance, as defined by Caudri et al. [30]. Additionally, FeNO and Rint measurements are used as secondary outcomes. Both techniques
have been well standardised for use in children older than 4 years by the American
Thoracic Society and the European Respiratory Society [55,56].

In the Netherlands, the Child Health Care physicians and nurses play a central role
in the early detection and counselling intervention of asthma symptoms in preschool
children because they have routine contact with about 90% of all preschool children
and their families [16]. In a well-regulated setting, administering a systematic early detection tool consisting
of parents' reports of the child's asthma symptoms (elicited via an interview by the
physician or nurse) may be an effective way of selecting children who might benefit
from asthma counselling, more detailed assessment at the child health centre, or referral
to an asthma nurse, GP or paediatrician.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

The study was initiated by HR and HJK, and they were responsible for acquiring the
study grant. ADM, JCJ, JCW, HJK and HR participated in the study concept and design.
ADM set up the cluster randomised controlled trial and was responsible for data collection,
data analysis and reporting the study results until June 2008. After June 2008 EH
had full access to all the data in the study and takes responsibility for the integrity
of the data and the accuracy of the data analysis and reporting the study results.
All authors reviewed and approved the final version of this manuscript.

Acknowledgements

This study is funded by the Netherlands Organisation for Health Research and Development
(ZonMw: project no. 22000128). The Generation R Study is conducted by the Erasmus
MC, University Medical Center Rotterdam, in close collaboration with the Child Health
Care Ouder & Kindzorg Rotterdam, the Rotterdam Homecare Foundation and the Stichting Trombosedienst & Artsenlaboratorium Rijnmond (STAR) Rotterdam. We gratefully acknowledge the contribution of all Generation
R participants and the health care workers at the participating child health centres
in Rotterdam, especially Inge Moorman, MD.

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(CHQ-PF28) in large random school based and general population samples.

Raat H, Landgraf JM, Oostenbrink R, Moll HA, Essink-Bot ML: Reliability and validity of the Infant and Toddler Quality of Life Questionnaire (ITQOL)
in a general population and respiratory disease sample.

Klassen AF, Landgraf JM, Lee SK, Barer M, Raina P, Chan HW, Matthew D, Brabyn D: Health-related quality of life in 3 and 4 year old children and their parents: preliminary
findings about a new questionnaire.

American Thoracic Society and European Respiratory Society: ATS/ERS recommendations for standardized procedures for the online and offline measurement
of exhaled lower respiratory nitric oxide and nasal nitric oxide.